Fix the stopping/pending message when launching a slave

It currently always says the slave is stopping when it's launching an
instance. The while loop and switch have been modified so the
appropriate logging message appears now.
Consider only slaves for the requested label when decrementing excessWorkload by number of pending spot instance slaves
Merge pull request #122 from Khan/master

Respect timeout=0 when launching slave agent, and restart slave when it dies.
Merge pull request #116 from jsternberg/fix-launch-instance-message

Fix the stopping/pending message when launching a slave
Merge pull request #117 from EverythingMe/JENKINS-25693

Resolve [JENKINS-25693] pending spot instance launch blocks launch of non-spot instances.